1. Field of the Invention
The present invention relates to a variable magnification copying apparatus, and more particularly, to an improved magnification converting mechanism for a variable magnification copying apparatus capable of effecting selected magnification, through manual alteration of lens positions with changing an original document scap speed of an optical system and to an improved scan speed changing mechanism for a variable magnification copying apparatus capable of changing an original document scan speed of an optical system.
2. Description of the Prior Art
Generally, when the image of an original document is magnified or reduced so as to copy the image on a sheet of paper, it is necessary to change not only a lens position but also the scan speed of an optical system to be applied thereto in response to the values of magnifications. Accordingly, in conventional variable magnification copying apparatuses, there are provided one drive means for changing a lens position and another drive means for scanning the image of the original document by the optical system, i.e., two kinds of drive means are necessary to carry out the above-described operations. In such an apparatus, one drive means is operated to change the position of a lens according to a selected magnification and the other drive means is controlled to change the scan speed of the image of the original document. A DC motor is generally used as the drive means for scanning the image of the original document, so that the number of rotations of the DC motor is controlled to change the image scan speed. Also, a variable magnification copying apparatus disclosed in Japanese Patent Laid-open Publication (unexamined) No. 165633/1985, is provided with a plurality of planet gears which rotate in unison with the rotation of an input shaft. The torque of the input shaft is selectively transmitted to a planet carrier which supports the axes of the planet gears through a spring clutch. The number of rotations of the output shaft is changed by selectively operating the planet gears which transmit the torque of the input shaft to the output shaft. When the planet gears which engage with gears mounted on the output shaft are selectively operated, the torque is transmitted to the planet carrier of the planet gears through the spring clutch. The operation of the spring clutch is controlled by changing the position in which a control pawl, provided with an arm operatively connected to a lever manually operated, contacts with a pawl provided with the spring clutch. With this construction, this apparatus is designed to make the construction of the speed change gears simpler with a manual selection of the scan speed, and to reduce the manufacturing cost.
However, the above-described variable magnification copying apparatus has disadvantages such as to render the construction in a large size at an expensive cost because a DC motor is used, which leads to the use of many motors including a lens drive motor. Although this construction can eliminate the need for installing a motor to scan the image of the original document by changing a scan speed manually, however, it is necessary to provide a motor which changes the lens position, and further, the lens position changing operation and the image scan speed changing operation are required to be made independently. Therefore, the apparatus is not compact and its cost is not so inexpensive. Moreover, the operation to change a magnification is complicated.
In addition to the above-described disadvantages, each time the image scan speed is changed, the planet gears and the spring clutch rotate, with the result that the pawl provided with the spring clutch contacts with the control pawl provided with the arm to generate a big noise. Furthermore, the torque to rotate the spring clutch, planet gears, and the planet carrier of the planet gears about the input shaft is great, which leads to the provision of a large main motor.